This invention relates to a device for cutting a selected part of a gel. Suitably, the gel may contain molecules, other than the gel molecules. Suitably, the gel may have been subjected to an electric field in an electrophoresis apparatus. Typical molecules include biological macromolecules, such as nucleic acids and proteins. The device of the invention is also adapted to eject the cut gel portion from the device. The molecules present inside the cut gel can be used in further work.
When a selected part of a gel is excised from the whole, a hole remains in the gel. Various hole producing devices are known in prior art, including those that are suitable for making holes in a gel. U.S. Pat. No. 2,463,455 to Dann describes a device that is able to make holes in agar gel in a circular pattern. U.S. Pat. No. 3,949,471 to Cawley discloses a device suitable for making wells or cavities in a gel. The gel material that has been cut is known to be removed by applying a vacuum, created by an external means, to the outer portion of the cutter. Once the cutting has been completed, the cut gel material can be discarded. U.S. Pat. No. 4,010,543 to Nusbaum teaches that holes can be made in a tacky material by using a hollow tube with a knob coupled to the top of the tube to form a handle. A hole in the knob vents the inside of the tube and therefore prevents formation of vacuum, and easy removal of the cut piece from the tube is facilitated. U.S. Pat. No. 6,035,750 to Hansen discloses a hole cutter with a vacuum slug removal means. Vacuum applied to the proximal end of the tube moves slugs away from the distal cutting end and through lumen of the tube. The removed slugs are then ejected at the proximal end of the hollow tube. The device of Hansen can be used as part of a medical catheter.
In U.S. Pat. No. 5,587,062 Togawa et al. a robotic apparatus for sample collecting from electrophoresis gels is disclosed. The apparatus contains a detector for optical detection of separated bands, a mechanism that moves a cutting tool, and a controlling device that directs cutting of a specific gel piece. The cutting tool allows packing of several cut gel pieces inside lumen of the cutting tool. A discharge mechanism, situated above the cutting tool, provides compressed air for ejection of the slug(s). Gel slug(s) packed inside the cutting tool is discharged into a container by means of compressed air that is supplied from the discharge mechanism.
Togawa et al. do not disclose which forces keep the cut gel inside the lumen of the cutting tool. It appears that the gel slugs remain inside the tube through frictional engagement with interior surface of the cutting tool. The strength of such frictional engagement depends on the properties of the gel material as well as on the properties of the inner surface of the cutting tool. Several different gel materials are currently in use for separating proteins and nucleic acids by gel electrophoresis. The most common ones are agarose and polyacrylamide. Reference is also made to several novel gels, including Poly(NAT) (U.S. Pat. No. 5,319,046), Clearose(trademark) (U.S. Pat. No. 5,541,255) and Spreadex(trademark) (U.S. Pat. No. 5,840,877. The above mentioned gel materials differ not only in their ability to separate nucleic acids and proteins, but also in their hardness and elasticity.
It has been found that cutting a piece out of each one of these gels can be done using a scalpel or a 0.2 mm thin nylon string. These tools, however, produce gel pieces of various sizes. As the gel volume varies, and since typical electrophoresis gels contain at least about 90% of water, this can create problems in subsequent steps, which may include, among others, incubation of a cut gel piece in a solution containing reagents of defined concentration. The concentration of these reagents then varies as the reagents are diluted with gel water to difference extents depending on the volume of gel that is excised. Furthermore, some practicing is needed to attain the skill necessary for handling the scalpel or the nylon string for this use.
Gel cutting can be also done using an ordinary pipette tip whose opening has been enlarged and sharpened prior to its use as a cutting tool. There is little variation in cut gel volume when using such a tip. The inner surface of the tip can be made rough by scratching it with a sharp metal, for example with the tip of forceps. The rough surface increases frictional engagement of the cut gel with the inner surface of the tip. In most cases, this improvised device worked well for cutting and recovery of a piece of Spreadexrm gel. That is, the cut gel piece remained inside the tip of the pipette after the tip was removed from the gel. However, this improvised device did not work with Clearose BG(trademark) gels. These gels are more elastic than Spreadexm gels and are substantially non-tacky. After lifting the tip out of the gel, the cut gel piece did not remain in lumen of the tip. Instead, it remained in its previous position in proximate association to the gel, even though it was completely cut from the surrounding gel. Evidently, frictional engagement between the cut gel and the tube surface was not sufficient to keep the cut gel in the lumen of the pipette. A device that overcomes the above described problems, as well as some other deficiencies of the devices known in prior art, is very desirable.
It is accordingly an object of the present invention to provide a novel gel cutting and recovery device that is suitable for cutting all gel materials.
It is an object of the present invention to provide an improved means of holding a cut gel piece inside a gel cutting device for its removal from association with the gel body.
It is a further object of the present invention to provide, in a single device, a means for creating reduced pressure sufficient to hold a piece of cut gel in the device, and a means for ejecting the cut gel.
Still a further object of the present invention is provision of a disposable device useful for cutting and recovery of a gel piece, containing proteins or nucleic acids, that have been separated by gel electrophoresis.
These and other objects, features and advantages will be explained, and will, in part, become clear from the following description in conjunction with the accompanying drawings.
In accord with an fulfilling these objects, the instant invention constitutes a novel device for cutting a portion of a gel; removing the cut portion of the gel from association with the gel body and enabling delivery of the cut gel portion from the device for further work on the cut gel portion. This device comprises a hollow first body and a piston second body at least partially disposed within and in longitudinally movable relationship to the hollow body. The hollow body has distal and a proximal ends, respectively. The distal end terminates in a cutting edge that at least substantially surrounds a smaller cross section hollow portion of the first body. The proximal end of the first body has a larger cross section hollow portion. A lumen connects the smaller and larger cross section hollow volumes. A first portion of the piston, that is proximate to the proximal end of the hollow first body, is so shaped and sized as to fit snugly in the lumen. A second portion of the piston has a cross section that is smaller than the cross section of the smaller cross section portion of the first body and is thereby adapted to longitudinally move freely within the smaller cross section portion of the first body. The second portion of the piston is longer than the length of the first portion of the hollow body. The snugness of the fit between the larger cross section portion of the piston and the second portion of the first, hollow, body is such that longitudinal movement of the piston body in relation to the hollow body will create a reduced or increased pressure, respectively, in the first hollow portion when the device is in cutting contact with gel material.